Energy suppliers in some European counties (such as Germany), for the purpose of electric-load leveling, are offering lower electricity rates to customers in exchange for permitting forcible shutoff of a power source for a heat-pump heater from outside (hereinafter referred to as a shutoff), under a contract with the customers, a predetermined number of times a day for a predetermined period of time (hereinafter referred to as a “shutoff hour”).
In this context, to respond to the control from outside as described above, the heat-pump hot water heater includes a relay switch which turns on and off the power source when receiving a ripple signal from an energy supplier.